Are you implying that we would assign a public /64 subnet to a collection of nanites that were designed to be absorbed after a week in the human body, and then retire that subnet forever? This seems like an unlikely scenario, but I'll assume it's just an intellectual exercise and take a stab!

- Total number of /64 subnets available: 2^64

- Total number of humans in this future: Let's say 16 billion (roughly twice what we're at now)

To get the total number of months before we'd run out of /64 subnets, assuming each human is absorbing one every month, we divide the number of /64 subnets by the number of humans:

2^64 / 16 billion =~ 1,152,921,505

Divide by 12 to get the total number of years:

1,152,921,505 / 12 =~ 96,076,792

So by my math, assuming the human population stayed steady at 16 billion (which seems just as absurd as the initial premise) we'd have about 100 million years to figure out how to start reusing some of those old subnets before we started running into trouble.

> Are you implying that we would assign a public /64 subnet to a collection of nanites that were designed to be absorbed after a week in the human body, and then retire that subnet forever?

No, I meant it as "You can reuse the subnet after 1 week + N" basically.

> it's just an intellectual exercise and take a stab!

Indeed it was, and thanks for conjuring a gratifying answer :)

IPv6 devotes a giant chunk of space to ephemeral link-local connections, if I recall correctly, at least a /64. So you'd need about 10^18 nanobots or so before you start to have to worry about link local address exhaustion.

These do not have to be globally unique, just unique on the local network.

Official assignments are at:

* https://www.iana.org/assignments/ipv6-address-space/ipv6-add...

Currently all public addresses are being assigned out of 2000::/3. The following are reserved for future (public?) use: 4000::/3, 6000::/3, 8000::/3, a000::/3, c000::/3.

Everything that starts with "f" is a special case, so the vast (vast) majority of address space is cleaved off.

I think this turns out to be a pretty good example of how stupidly big the ipv6 space is. Because it sounds like a big ask until it meets the numbers.

So you want "even billions(!!1!)" of nanobots per allocation. Well I'm lazy, and dynamically allocating a /64 is built right into the protocol. So lets let my medication dynamically allocate out of a /64. How many billions? Billions of billions. So lazy, so sorted.

But of course, I don't want my medication talking to my wife's medication. So lets de-conflict that. In fact, let's de-conflict everyone's medication.

We all know that 32bits is a bit over 4 billion. So 33 bits is going to be a bit over 8 billion. That's enough for now, but it's iffy, so let's go for 34bits, a bit over 16 billion. But in ipv6 world, it's polite to land on a nibble-boundary, so we'll go for 36 to be polite.

I'm going to steal the old allocation for ULA as an example. It was /7, but I'm going to call it /8 because I like round numbers.

So lets have an 8-bit prefix ala ULA. Then an 8bit planet number. Then an 8bit country/healthservice/issuingbody number. Then a 40bit human number, because I ran out of reasons to waste 8's There's our 64bit network number. With 64 bits left for billions of billions of nanobots to dynamically allocate.

The best bit about ipv6 isn't billions, it's that we get to actually structure our networks instead of cramming them into every nook and cranny we can buy.